This invention relates to a propeller actuation system for an aircraft. More particularly, the invention relates to a system and method of storing hydraulic fluid in a auxiliary tank for use in changing the pitch of a propeller blade.
Aircraft having propellers typically include a propeller actuation system for changing the pitch of the propeller blades during in-flight conditions and ground maintenance conditions. The blade pitch is typically changed using a main hydraulic pump driven by a gearbox mechanically connected to an engine that drives the propeller. Fluid from a main tank is provided to the main hydraulic pump, which supplies the fluid to a propeller control system that changes the blade pitch. The main hydraulic pump and main tank are used during normal in-flight operation of the aircraft.
Conditions arise in which it is undesirable or difficult to use the main hydraulic pump and main tank to change the blade pitch. For example, during an in-flight condition in which the main hydraulic pump becomes inoperable or the system associated with the main tank becomes inoperable, an auxiliary control system is used to change the blade pitch. In the example of an engine failure, the auxiliary pump, which is fed by an auxiliary tank, supplies fluid to the propeller control system to move the blades to a feather position for emergency aircraft operation.
The auxiliary control system may also be employed during ground maintenance procedures. For example, it may be desirable to move the blades from a feather position to a reverse position and back to a feather position to exercise the blades or place the blades in a position that provides access to the propeller and other components for service.
The auxiliary tank of the auxiliary control system provides a volume sufficient to store fluid needed during in-flight and ground maintenance conditions to effectuate a desired change in blade pitch. Prior art systems have employed a large auxiliary tank to provide the needed volume of fluid. The auxiliary tank was filled with fluid from a lube system of the gearbox, which is not replenished if the gearbox is not driven by the engine. As a result, there is a need for a large auxiliary tank to account for conditions in which the engines is not running and a change in blade pitch is desired. Large auxiliary tanks create weight and packaging penalties for the aircraft.
What is needed is a reduced size auxiliary tank and a propeller actuation system designed to supply the desired volume of fluid to the auxiliary tank without compromising the ability to change blade pitch during in-flight and ground maintenance conditions.